This invention relates generally to internal combustion engines that propel motor vehicles and are equipped with variable valve actuation. In particular the invention relates to a control strategy for cylinder valve actuation that facilitates cold cranking, starting, and warm-up of such an engine, especially a diesel engine.
Starting of a diesel engine requires significant effort because of the high compression ratio that is inherent in such an engine. Cold temperatures compound the effort. In an automotive vehicle having a diesel engine as the prime mover, the use of cold-start aids such as glow plugs and intake air heaters may be necessary to start the engine. The electric starter motor for turning the engine over must be sufficiently powerful both to compress charges in the engine cylinders and to overcome the relatively substantial resistance torque that the kinematic mechanism of the engine imposes when the engine is cold.
The creation of an engine and an operating strategy that can facilitate engine cranking and starting, especially when the engine is cold, is therefore seen to be a desirable objective. The present invention seeks that objective through the use of a variable actuation mechanism for engine cylinder valves and of an engine control system embodying solid-state electronics that are processor-based. The processor can process certain data inputs to develop data outputs defining valve opening and closing times that are most appropriate to the inventive strategy. The data outputs are converted into electric signals that are delivered via electric circuits to actuators of the variable valve actuation mechanism.
Because certain principles of the present invention include changing the time in the engine operating cycle when the intake and exhaust valves for the engine cylinders open and close, the variable valve actuation mechanism of the engine must be effective on each such cylinder valve. An example of such a mechanism comprises an electric actuator for opening and closing each corresponding cylinder valve in accordance with the electric signal applied to the actuator. This type of engine is sometimes referred to as a camless engine.
A primary aspect of the present invention relates to a novel strategy for controlling the timing of the opening and closing of both cylinder intake and cylinder exhaust valves in an internal combustion engine that has a variable valve actuation mechanism for operating those valves, especially controlling the valve timing when the engine is being cranked and started while cold.
One aspect of the present invention relates to a novel strategy for an internal combustion engine, especially a compression ignition, or diesel, engine that has a variable valve actuation mechanism for varying the timing of cylinder intake and exhaust valves. The disclosed strategy is implemented via an electronic engine control that processes input data representing values of certain parameters that are relevant to engine operation, including parameters relevant to control of the timing of opening and closing of the cylinder valves in accordance with principles of the invention. Data for operating the variable valve actuation mechanism is processed according to a software algorithm that is executed by the control to develop output data representing desired timing for opening and closing the cylinder valves. The data is converted to signals suitable for operating electric actuators of the variable value actuation mechanism to open and close the cylinder valves.
One general aspect of the claimed invention relates to a method of cranking and starting a multi-cylinder internal combustion engine at an engine temperature that is substantially below a range of engine operating temperatures within which engine operation will eventually stabilize after the engine has been running for an amount of time sufficient to bring its temperature within that temperature range. The engine has a kinematic mechanism, including pistons that reciprocate within the cylinders, through which energy of combustion occurring within the cylinders is converted to a torque output. A variable valve actuation mechanism varies the opening and closing times of intake and exhaust valves that control flow between the cylinders and the respective intake and exhaust systems.
The method comprises: a) cranking the engine while not fueling the cylinders and while operating the variable valve actuation mechanism to cause the pistons in at least some of the cylinders to operate at an initial effective compression ratio for initial cranking that is less than an effective compression ratio for running when the engine is eventually fueled and runs under its own power; b) then, while continuing not fueling the cylinders, operating the variable valve actuation mechanism to cause the pistons in those cylinders that are operating at the initial effective compression ratio to draw charge air through a respective intake valve and compress the drawn charges to an increased effective compression ratio that is greater than the initial effective compression ratio and to exhaust the compressed charges through a respective exhaust valve into the exhaust system; c) then operating the variable valve actuation mechanism to cause the pistons in those cylinders to continue operating at the increased effective compression ratio while commencing to draw a portion of their charges from the exhaust system through the respective exhaust valve; and d) then commencing the fueling of less than all of the cylinders while operating the variable valve actuation mechanism to operate the intake and exhaust valves of the cylinders being fueled to cause the engine to start running under its own power.
Another aspect relates to an engine embodying a control for performing the foregoing method.
Another general aspect of the claimed invention relates to a method of cranking a multi-cylinder internal combustion engine prior to fueling any cylinder. The method comprises: a) cranking the engine while operating the variable valve actuation mechanism to cause the pistons in at least some of the cylinders to operate at an initial effective compression ratio for initial cranking that is less than an effective compression ratio for running when the engine is eventually fueled and runs under its own power; b) then operating the variable valve actuation mechanism to cause the pistons in those cylinders that are operating at the initial effective compression ratio to commence drawing charge air through a respective intake valve and operate at an increased effective compression ratio that is greater than the initial effective compression ratio and exhausting compressed charge air through a respective exhaust valve into the exhaust system; and c) then operating the variable valve actuation mechanism to cause the pistons in those cylinders to continue operating at the increased effective compression ratio while commencing to draw a portion of their charges from the exhaust system through the respective exhaust valve.
Another aspect relates to an engine embodying a control for performing the foregoing method.
Still another general aspect of the claimed invention relates to a method of cranking and starting a multi-cylinder internal combustion engine at a starting engine temperature and then running the engine to a running engine temperature that is substantially greater than the starting engine temperature. The method comprises: a) cranking the engine while the cylinders are not being fueled and while operating the variable valve actuation mechanism to cause the pistons in at least some of the cylinders to operate at an initial effective compression ratio for initial cranking that is less than an effective compression ratio for running when the engine is eventually fueled and runs under its own power; b) then, while the cylinders continue not to be fueled, operating the variable valve actuation mechanism to cause the pistons in those cylinders that are operating at the initial effective compression ratio to commence drawing charge air through a respective intake valve and operate at an increased effective compression ratio that is greater than the initial effective compression ratio and exhausting compressed charge air through a respective exhaust valve into the exhaust system; c) then operating the variable valve actuation mechanism to cause the pistons in those cylinders to continue operating at the increased effective compression ratio while commencing to draw a portion of their charges from the exhaust system through the respective exhaust valve; d) then commencing the fueling of at least some of the cylinders and operating the variable valve actuation mechanism to operate the intake and exhaust valves of the cylinders being fueled to start the engine running under its own power; and e) operating the variable valve actuation mechanism to advance the timing of opening of the exhaust valves from what that timing will become once the engine has attained running temperature and to change that timing as a function of engine temperature as the engine temperature approaches running temperature.
Another aspect relates to an engine embodying a control for performing the foregoing method.
Yet another general aspect relates to a method of starting a multi-cylinder internal combustion engine at a starting engine temperature and then running the engine to a running engine temperature that is substantially greater than the starting engine temperature. The method comprises: a) before fueling the cylinders, operating the variable valve actuation mechanism to cause the pistons in at least some of the cylinders to commence drawing charge air through a respective intake valve, compress the charge air, and exhaust the compressed charge air through a respective exhaust valve into the exhaust system; b) then operating the variable valve actuation mechanism to cause the pistons in those cylinders to commence drawing a portion of their charges from the exhaust system through the respective exhaust valve; c) then commencing the fueling of those cylinders and operating the variable valve actuation mechanism to operate the intake and exhaust valves of those cylinders to start the engine running under its own power; and d) then operating the variable valve actuation mechanism to decrease the amount of advance in the opening time of the exhaust valves of those cylinders as engine operating temperature increases.
Another aspect relates to an engine embodying a control for performing the foregoing method.
Still another general aspect of the invention relates to a method of starting a multi-cylinder internal combustion engine at a starting engine temperature and then running the engine to a running engine temperature that is substantially greater than the starting engine temperature. The method comprises, before fueling cylinders of the engine, operating a variable valve actuation mechanism to cause pistons in at least some of the cylinders to commence drawing charge air through a respective intake valve, compress the charge air, and exhaust the compressed charge air through a respective exhaust valve into the exhaust system. Then the variable valve actuation mechanism operates to cause the pistons in those cylinders to commence drawing a portion of their charges from the exhaust system through the respective exhaust valve, and when fueling is subsequently commenced, operates the intake and exhaust valves of those cylinders to start the engine running under its own power. The variable valve actuation mechanism then operates to decrease the amount of advance in the opening time of the exhaust valves of those cylinders as engine operating temperature increases.